If you have installed a leak which is a higher version than your carrier has pushed, you need to use a workaround as follows.

1. Close Blackberry Link
2. www.blackberry.com/updates in Microsoft Internet Explorer
3. Detach all BBs from your computer
4. Click on the check for updates button
5. Connect the device in question switched on.
6. Whilst connected, turn the device off.
7. Once completely off, turn the device on again
8. As soon as it is available on your computer screen, click the ok button in the dialogue box.
9. After a while the LED on your device will be green and the computer screen should give the option to install the stock os.

this worked for me, but sometimes the connection process took a few attempts!